It is known to produce combustible shaped ammunition components from cellulose and nitrocellulose fibers (and synthetic fibers) by using synthetic resin binders, e.g., polyurethanes, according to known felting methods. In the known method, pentaerythrityl tetranitrate or trimethylenetrinitroamine can be incorporated to improve the combustibility of the compositions. All the components (possibly with the exception of the binder) are suspended in water and wet webs (i.e., crude blanks or preforms) are produced from the suspension thus formed by dipping a shaped form or "negative" into an aqueous suspension of the fibers and depositing the fibers on the form by the use of suction. The webs thus obtained are dried and compressed in heated presses and trimmed to measure. When the binder cannot be added to the suspension, it is introduced by impregnation of the pressed component. The blanks and therefore the final dry products produced according to this method are necessarily homogeneous in composition because of the nature of the production method employed.
However, in testing these combustible ammunition components, it was found that a residue-free combustion of the component depends frequently to a great extent on the pressure produced during firing, on the firing temperature, and on the temperature of the gas produced by the powder. This is of particular importance in charge containers from which different propellant charges are fired. Moreover, the fact that cartridge cases are subjected to combustion within the powder chamber of a gun has an effect on the extent to which these cases are transformed into gases, because the bottoms of cartridge cases in the powder chambers of guns burn more difficulty than the open ends of cartridge cases.
The finding that the powder chamber of tubular weapons (e.g., guns) cannot be considered a uniform reaction chamber (so far as the combustion of cartridge cases therein is concerned) means that ammunition components of homogeneous composition are not successful because their composition must be adjusted to the least favorable combustion conditions in the powder chamber in order to positively avoid the presence of residues. Better combustion properties require, for example, a higher proportion of nitrocellulose (and/or a lower proportion of binder) in the container. This, in turn, means that the cartridge possesses an undesirably high flammability and/or lower mechanical properties.
Uniformity in the material structure of the walls of the wet web (and therefore the finished product) is likewise not practical for the following reasons. In order to provide the desired degree of flammability, water vapor permeability, and water absorptivity in any instance, the final products (when of homogeneous composition) must be subjected to a more or less considerable after-treatment by painting or impregnation. These steps generally reduce, however, the combustibility of the finished product.
Up to the present it has been impractical to provide an ammunition component which is of adequate mechanical strength throughout, because to meet this requirement, the composition of the zones under greater mechanical stress must be altered, for example by the addition of strengthening fiber material, so that combustibility of the component as a whole is decreased. It follows, therefore, that it is a determinant advantage if the composition of zones of the ammunition component can be varied at will, since this possibility permits the composition and therefore the strength/combustibility relationship in the respective zones to be optimized.
Since this was not possible by present production methods (where the blank is produced from a suspension of uniform composition by immersion of a hollow form into a fibrous suspension and with suction applied to the form), portions of the ammunition component (e.g., bottom pieces and upper parts, where a different composition was necessary) had to be produced as separate units which were then cemented together to form the finished component. This was unsatisfactory because of the added work involved and since the cemented joints and overlappings which are necessarily present do not burn or explode in the same manner (i.e., as completely) as the main body of the component.